The number of page types, however large, is finite. The contents
however (take, for example, eBay) is infinite.
Another solution is to identify the primary (or most-used) pages and test those most.
If a dynamic server page scripting engine is used, and it fails, it will stop the entire site until restarted.
A failed individual CGI script will simply affect an individual browser session.
5.5.10 Web Reliability Testing
There are two main sources of unreliability in a website:
1. The browser??“web server connection (discussed below)
2. Everything else (see section 16.8)
Web performance is a bit like the quality of life. You know if it??™s ever mentioned that it??™s either bad or
non-existent. You need to be able to calculate it. Here??™s the process:
1. Draw a reliability block diagram of your system. It could look something like the diagram in Figure 5.5.
Testing and the Web 79
2. Identify the possible paths. Each element of the diagram (Browser (Br), Internet (In), firewall (Fi),
web server (We), application objects (Ap), banking application (Ba), legacy application (Le), and
database server (Da)) has some level of reliability. That is: there is a probability of failure once
every so many years, days, minutes, or seconds. A request goes from browser to:
??? Web server
??? Legacy application
??? Database server, or
??? Banking application.
Thus to calculate the probability of a request going to the legacy application and back, failing over
(say) 1 hour we can (with reference to section 18.
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